This invention relates generally to balancing vehicle wheels and more particularly, to methods and systems for balancing vehicle wheels using a balancer that includes a balance weight placement aid.
At least some known automotive wheel balancer manufacturers offer a feature which illuminates a portion of the wheel assembly to indicate a location for the application of balance correction weights. U.S. Pat. No. 6,244,108 to McInnes, et al. describes a wheel balancer for balancing a wheel. A telescoping extendible sensor arm physically detects adhesive balance weight receiving locations on a rim of the wheel at desired balancing planes. The adhesive balance weight receiving locations are indicated by a laser light source which directs a laser dot at the rim to thereby indicate to an operator the precise position at which the correcting balance weight is to be attached to the rim.
U.S. Pat. No. 6,484,574 to Douglas et al. describes a wheel balancer including a rim measuring apparatus configured to scan the inner surface of the wheel rim/tire assembly. The optimum plane locations, amounts of correction weights, and the number of correction weights, are calculated by a control circuit to result in a minimized residual static and dynamic imbalance. The control circuit utilizes a motor drive to automatically index and hold the wheel at the proper rotational position for placement of an adhesive imbalance correction weight, and a laser pointer illuminates the surface of the rim at the axial position of the weight imbalance correction plane at which the imbalance correction weight is to be applied.
A Coats Model 1250 Wheel Balancer is described as Coats Model 1250 having a Laser Guided Operation™ for placing adhesive weights to an inner rim of a wheel. The balancer includes a laser dot that is positionally adjustable using a manual laser locator knob to a desired weight location. The balancer also includes a manually activated line laser that displays a line of laser light along an inner circumferential span representing the balance plane on an inner surface of the wheel rim near a bottom dead center position for locating the laser dot on the balance plane. The intersection of the dot and the line indicates the adhesive weight placement location. These totally-manual lasers must be positioned by the operator and are not controlled by the Coats Model 1250 Wheel Balancer.
But such adhesive weight placement aid systems do not address the modes of balancing which require clip style weights to be attached at the rim lip to tire interface. Clip weights are typically installed at “Top Dead Center” (TDC), which is straight up from the center of the wheel (12 o'clock position). But because the user cannot easily position himself to view these locations “straight on,” it is very difficult to judge accurately where TDC physically is. The viewing angle of the operator to the wheel can result in TDC placement errors. Placement errors as small as can ¼ inch can cause significant residual static imbalance that is directly proportional to the weight size, yet placement errors as high as ¾ inch from TDC have been observed in actual usage in shops.
CEMB of Italy describes their model C40 Professional balancer in an advertising bulletin from approximately 1996. The C40 Professional projected a sheet of incandescent light onto the TDC tread portion of a tire mounted onto the balancer. The machine had no provisions for automatically holding the wheel at the balance position. The TDC tread of the wheel assembly was continuously illuminated and the bulletin does not describe turning on the light when the correction weight location was at TDC, or any control of the light by the wheel balancer. The illumination also did not provide indication to the operator which plane was being serviced since the line covered the entire top surface of the tire tread. Also, the sidewall bulge of most tires would prevent the light source from striking a line at the actual location of the clip weights on the wheel rim. The user in most cases would be observing a line on top of the tire when he really needs it on the sidewall where it intersects the rim, which could be several inches away. This could result in significant weight placement errors.
The weight placement error and residual static imbalance problem is even worse when using adhesive weights when the aforementioned adhesive weight placement aid systems do not exist on the wheel balancer (these systems can be expensive or considered to be cumbersome to operate). Adhesive weights are typically mounted at TDC or at BDC and either location is extremely difficult to judge. For TDC the user must work “upside down”, contorting himself in the process. For BDC the balancer's mounting shaft is in the way of getting a straight down view at the weight location. A method of minimizing imbalance is needed for all instances of weight placement methods available without causing any residual static imbalance after placing the correction weights.